aha srry i didn't notice it "readonly"
and what do you want to achieve?? to reload the page by each pressing of "+" (resp."-") ?
if so then "+"buton could look like ( analogical the "-" button)
<a rel="nofollow" class="cart_quantity_up btn btn-default button-plus" id="cart_quantity_up_{$product.id_product}_{$product.id_product_attribute}_{if $quantityDisplayed > 0}nocustom{else}0{/if}_{$product.id_address_delivery|intval}" href="{$link->getPageLink('cart', true, NULL, "add=1&qty={if $product.minimal_quantity > 0}{$product.minimal_quantity}{else}1{/if}&id_product={$product.id_product|intval}&ipa={$product.id_product_attribute|intval}&id_address_delivery={$product.id_address_delivery|intval}&token={$token_cart}")|escape:'html':'UTF-8'}" title="{l s='Add'}"> <span><i class="icon-plus" style="padding:.7em;"></i></span></a>